本文選題：信道編碼 + 準循環(huán)LDPC碼　； 參考：《西安電子科技大學》2014年碩士論文

【摘要】：目前科學技術發(fā)展迅猛,其中高清晰電視、視頻會議、遠程監(jiān)控以及遙感成像等技術得到廣泛應用,人們生活中的信息交流已經主要依靠于多媒體通信。而通信系統(tǒng)往往會受到噪聲干擾,使得無線信道中傳輸?shù)膱D像質量大大下降,尤其是深空通信有著超遠的傳輸距離、超復雜的傳輸環(huán)境以及自身設備及能源嚴格受限等特性,對信道糾錯編碼等關鍵技術提出了較高的要求,因此學習研究信道編碼的意義深遠。隨著稀疏圖碼與譯碼中迭代理論的研究與實現(xiàn),LDPC(低密度奇偶校驗碼)漸漸受到普遍關注,它性能逼近香農限、實現(xiàn)復雜度低、譯碼算法可并行且描述簡單,因此LDPC碼已經應用于各種新的通信標準。其中,有著獨特奇偶校驗矩陣結構的準循環(huán)LDPC碼,能夠實現(xiàn)具有線性復雜度的編碼,是一種得到了廣泛應用的結構化LDPC碼。1)本文對于基于歐式有限幾何方法構造的準循環(huán)LDPC碼進行了深入研究,設計了CCSDS標準的基礎(8176,7154)準循環(huán)LDPC碼,并進行了實驗仿真與分析。實驗結果說明,與對應的隨機LDPC碼相比,合理構造的準循環(huán)LDPC碼在編譯碼復雜度大大降低的基礎上基本沒有損失性能。另外,對于迭代次數(shù)對譯碼性能的影響做了基礎研究。2)由于準循環(huán)LDPC碼被廣泛應用于各種實際工程,高效譯碼算法的重要性便體現(xiàn)出來。本文在研究了BP算法、LLR-BP算法、MS算法等基本譯碼方法的基礎上深入探討并實現(xiàn)了SBP算法以及其改進算法的實驗仿真。結果說明,改進的SBP算法不僅在譯碼性能上略占優(yōu)勢,還降低了運算復雜度,提高了收斂速度。最后分析了譯碼錯誤產生的原因并綜合考慮了系統(tǒng)性能的需求以及硬件資源,提出了一種改進的多點最小和算法并進行了實驗仿真。該算法在很少增加復雜度的前提下,提高了譯碼算法的性能,減少了平均迭代次數(shù),因此適合于對誤碼率性能和譯碼速度均有嚴格要求的高吞吐量LDPC碼譯碼器的使用。3)最后針對CCSDS庫中遙感圖像的傳輸問題,提出了一種基于LDPC碼的等差錯保護遙感圖像傳輸方案。此方案對原始遙感圖像先進行小波變換分析,再根據(jù)嵌入式分塊的方法進行信源編碼。信道編碼則運用基于LDPC碼的聯(lián)合編碼來對嵌入式分塊編碼過后的輸出碼流進行同等程度的保護,使得碼流的抗干擾能力得到提高。實驗結果說明,相比于傳統(tǒng)的RS、Tornado碼,遙感圖像的傳輸在此方案中更為可靠。最后本文總結了以上研究內容,并且針對準循環(huán)LDPC的編譯碼均提出了改進的方向。
[Abstract]:With the rapid development of science and technology, high-definition television, video conferencing, remote monitoring and remote sensing imaging are widely used. The communication of information in people's lives has mainly depended on multimedia communication.However, the communication system is often disturbed by noise, which makes the image quality in wireless channel decline greatly. Especially, the deep space communication has the characteristics of ultra-long transmission distance, ultra-complex transmission environment, strict limitation of its own equipment and energy, and so on.The key technologies such as channel error correction coding are required, so it is of great significance to study channel coding.With the research and implementation of iterative theory in sparse graph code and decoding, LDPC (low density parity check code) has been paid more and more attention. Its performance is close to Shannon limit, the complexity of implementation is low, the decoding algorithm can be parallel and simple to describe.Therefore, LDPC codes have been applied to various new communication standards.Among them, quasi-cyclic LDPC codes with unique parity check matrix structure can realize coding with linear complexity.It is a widely used structured LDPC code. 1) in this paper, the quasi-cyclic LDPC codes based on the Euclidean finite geometry method are studied in depth, and the quasi-cyclic LDPC codes based on the CCSDS standard are designed, and the experimental simulation and analysis are carried out.The experimental results show that compared with the corresponding random LDPC codes, the reasonably constructed quasi-cyclic LDPC codes have no loss of performance on the basis of greatly reducing the complexity of encoding and decoding.In addition, the influence of iteration times on decoding performance is studied. 2) because quasi-cyclic LDPC codes are widely used in various practical projects, the importance of efficient decoding algorithm is reflected.Based on the study of the basic decoding methods such as the BP algorithm and the LLR-BP algorithm and MS algorithm, this paper discusses and implements the SBP algorithm and the experimental simulation of its improved algorithm.The results show that the improved SBP algorithm not only has a slight advantage in decoding performance, but also reduces the computational complexity and improves the convergence speed.Finally, the causes of decoding errors are analyzed, and the requirements of system performance and hardware resources are considered synthetically. An improved multi-point minimum sum algorithm is proposed and the experimental simulation is carried out.The algorithm improves the performance of the decoding algorithm and reduces the average number of iterations without increasing the complexity.Therefore, it is suitable for high throughput LDPC decoder with strict performance and decoding speed. Finally, an equal-error protection remote sensing image transmission scheme based on LDPC code is proposed to solve the problem of remote sensing image transmission in CCSDS library.In this scheme, the original remote sensing image is analyzed by wavelet transform, and then the source coding is carried out according to the embedded block method.Channel coding uses joint coding based on LDPC code to protect the output bitstream after embedded block coding to the same degree, so that the anti-jamming ability of bitstream is improved.The experimental results show that the transmission of remote sensing images is more reliable than that of the traditional RSU Tornado code.Finally, this paper summarizes the above research contents, and proposes the direction to improve the encoding and decoding of quasi-cyclic LDPC.
【學位授予單位】：西安電子科技大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN911.22

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